The Re-entry Balloon
One big problem with executing a controlled descent and landing from any great altitude is the effect of adiabatic heating on a descending balloon.
As a balloon descends, the gas in the balloon heats by compression. In the troposphere the resulting imbalance in gas temperature is mitigated by the natural temperature gradient in the atmosphere. As the balloon descends the gas in it warms, which yields excess lift, as in a hot air balloon. In the lower regions of the earth's atmosphere, the troposphere, the air is warmer at the low altitudes. But, depending on the gas in the balloon, the dry adiabatic lapse rate of the gas can even exceed the ambient gradient. This gives transitory thermal lift (TTL) and slows or even prevents descent. The phenomenon is accentuated in the stratosphere where there is little or no temperature gradient.
With the use of plastic film balloons and helium for ascensions much higher than that of Explorer II the effect can be almost, if not, catastrophic. In order to force the descent against the TTL a great deal of gas must be vented. All of that excess venting must be counteracted by ballasting at lower altitudes when the gas comes into equilibrium with ambient conditions. In fact these ballasting requirements normally exceed the possible availability of adequate ballast. Hence, in practice, uncontrolled descent and landings have been common even in the case of flights to the mid stratosphere.
This problem has been considered to be the limiting factor on the state of the art.
XAP conquers this problem by utilizing a hot air balloon component to the aircraft that can assume control on descent. The weight penalty of carrying the hot air module and its fuel and heating systems is far less than the unattainable ballast envisioned above. This hot air module is also utilized during the launch and early climb sequences of the XAP flights. This minimizes the stress on the film gas cells at launch and through the first half of the climb through the atmosphere. (Fuel used during the flight up to the 500 milibar level is considered as ascent ballast. Tankage for that sequence is parachuted off after the burners are shut down.)
The hot air module is built into the flight train, between the pressure cabin and the suspension lines to the gas cells. Unlike the common sport balloons, this balloon has a rigid mouth and rigid connection to the cabin to facilitate instant ram air inflation during descent.
The hot air module and the pressure cabin are reusable, while the plastic film gas cells are disposable with each mission.
Post XAP expedition tours with the hot air balloon, complete with our "Title Sponsor" logos are anticipated. It will be suitable for exhibition worldwide and participation in all the world's great balloon fiestas and sport events.